The present invention relates to a rotary-type fluid energy convertor particularly utilized as fluid pump or motor operated by static pressure.
Conventionally, there has been the practical application of rotary-type fluid energy convertors of the so-called "swash plate type or bent axis type" as a hydraulic pump or motor in which a pressure is converted into a driving torque.
In the rotary-type fluid energy convertors of the described type, the conversion of the pressure into the driving torque is carried out between the reciprocating motion and the rotating motion of a piston. And it is therefore necessary to arrange a complicated mechanism such as a cam mechanism and a link mechanism on the side of a rotary body. In addition, since the axis of the rotary body is inclined with respect to a direction of operation of a piston at a portion where the pressure is converted into the driving torque, a force in a direction inclined with respect to the rotating axis is applied to a coupling portion, i.e. roller bearing, between the piston and the rotary body. Therefore, it is necessary for the roller bearing to have an increased strength, resulting in a large structure at that portion, in the lowering of the lifetime of the roller bearing and in the increase of an energy loss, which are significant problems for a fluid pump or motor of the character described above.
In order to obviate these problems or defects, the inventor of this application conceived an improved rotary-type fluid convertor such as disclosed in Japanese Patent Publication No. 64-8190 (8190/1989) as well as Yasuo Kita, "YUATSU TO KUKIATSU" Vol. 20, No. 2 (March 1989), pp. 107-708. This improved rotary-type fluid energy convertor comprises: a first annular member; a second annular member mounted so as to be relatively rotatable on the inner peripheral surface of the first annular member through first static pressure bearings arranged intermittently in the circumferential direction of the first annular member; a plurality of seal bushings disposed at portions corresponding to the respective first static pressure bearings, each of the seal bushings having a front end located at the inner peripheral surface of the second annular member through a second static pressure bearing; a seal bushing holding member disposed at a portion eccentric with respect to the first and second annular members so as to form spaces having inner volumes on the bottom side of each seal bushing varies in response to the relative rotation between the first and second annular members; and paired fluid passages communicated respectively with spaces having inner volumes being increased and being decreased.
In such a fluid energy convertor, pressure guide passages are formed by the seal bushings and pressure guide passages are provided for the second annular member. The fluid filling in the respective spaces is guided into the first and second static pressure bearings through the corresponding pressure guide passages in such a manner that the static pressure of the fluid guided into the respective first static pressure bearings and the static pressure of the fluid guided into the respective second static pressure bearings are made resistive in accordance with the driving torque acting on an input-output shaft of the rotary body by the sum of the couple of forces acting to the second annular member.
According to the structure of the fluid pump or motor described above, a heavy load bearing is eliminated so that a compact and lightweight energy convertor can be realized, and which is capable of maintaining a predetermined performance in a long time period. Furthermore, the energy convertor can utilize a fluid having a low viscosity and can achieve a smooth operating condition from a stopping time to a high speed operation starting time.
However, according to the described fluid energy convertor, since it is necessary that the first and second annular members and other members located in association with these annular members all have tapered structures, it is necessary for the sliding portions between these members to be inclined with respect to the axis of the rotary body, which requires a troublesome working processes. Furthermore, since it is necessary to construct the first static pressure bearing so as to have a large diameter, the sliding speed thereof should be made fast, thus being inconvenient in view of energy loss or setting of a high speed limit.